The present invention relates to a process for concentrating aqueous epigallocatechin gallate (hereinafter abbreviated to EGCG) solutions. In particular the invention relates to a process for concentrating aqueous EGCG solutions using selective nanofiltration or reversed osmosis membranes (herein abbreviated to membrane).
Ekanayake et al., U.S. Pat. No. 5,879,733 (xe2x80x9cEkanayake ""733xe2x80x9d) describes a process for the preparation of green tea extract having improved clarity and color. These extracts are obtained by treating an aqueous green tea extract with an amount of a food grade cation exchange resin effective to remove metal cations present in the extract. The extract treated with a cation exchange resin is then contacted with a nanofiltration membrane to remove the higher molecular weight materials such as e.g. pectins, proteins, chlorophyll and oxidation products.
The nanofiltration membranes described in Ekanayake ""733 are made from polymers having a molecular weight cut off from about 700 to about 5000 Daltons (corresponding to pore sizes in the range of from about 17 to about 40 Angstroms). Polymers such as cellulose acetates, polysulfones, and polyvinylidenefluorides are used for making these nanofiltration membranes. Especially disclosed is the use of an OSMO SP-12 nanofiltration membrane (made by Osmonics, Inc. of Minnetonka, Minn.). The cellulose acetate polymer from which the membrane is made has a molecular weight cut off of 1000 Daltons (corresponding to a pore size of about 20 Angstroms). By use of the membrane, the tea catechins, which have a molecular size smaller than the pore diameter of the membrane pass through the membrane together with water, while the higher molecular weight materials are rejected by the membrane.
Ekanayake ""733, however, does not disclose a membrane which is suitable to concentrate aqueous EGCG solutions. Thus, there is still a need to find a membrane that has both a high retention rate of EGCG, and is able to maintain an acceptable flow rate of the permeate stream.
One embodiment of the invention is a process for concentrating an aqueous epigallocatechin gallate (EGCG) solution. This process includes feeding an aqueous EGCG solution having a dissolved solids content of about 0.03 wt % to about 10 wt % to at least one membrane module under a pressure of about 5 bar to about 100 bar to provide a permeate purge and a retentate return wherein the concentration of EGCG is increased in the retentate return relative to the concentration in the feed solution and whereby the membrane is characterized by a retention coefficient for EGCG of over 90%, collecting the permeate purge, and collecting the retentate return.